In the prior art, air cooling arrangements consist of modules having heat sinks, such as fins, attached to the top side thereof, as shown in FIG. 2 of U.S. Pat. No. 3,993,123 which issued Nov. 23, 1976. These modules are used in an array within the computer frame, with air being blown thereover parallel to the plane of the fin, similar to what is shown in the controlled bypass configuration for air-cooled computer frames, Vol. 21, No. 6, November 1978, IBM Technical Disclosure Bulletin (TDB). As can be seen, the arrangement is a push-pull air cooling scheme with a blower pulling at the top and a blower pushing at the bottom. This is the conventional air cooling arrangement used in many large scale computers. It should be appreciated that the air received at the bottom module is cooler than that received at the top module, since the air at the top module contains all the hot exhaust air from the below lying modules. The particular arrangement shown in the TDB uses a frontal bypass configuration to provide a direct path from the bottom blower to board row 3 of the frame, and a further direct bypass path from the row 3 to the upper blower. This bypass arrangement provides increased air flow to the middle board row 3 of the frame which has always experienced higher temperatures due to lower air flow in present air-cooled systems.
The IBM Technical Disclosure Bulletin, Vol. 14, No. 2, July 1971, shows an air cooling scheme which utilizes a double pull air flow arrangement. This arrangement shows the air entering at the middle gate 12 and separating, half to flow up and half to flow down. The air essentially flows over the boards and components parallel thereto. Thus, the usual temperature differential .DELTA.t along the column of gates is cut in half since a .DELTA.t exists from the middle gate to the top gate and from the middle gate to the bottom gate.